This invention relates to new and useful ultraviolet radiation sunscreen agents and compositions and to methods of protecting the human skin against the potentially harmful effects of sunlight.
It is well documented that human skin is sensitive to sunlight containing radiation of wavelengths between about 290 nanometers (nm) and 400 nm as well as artificial light. Ultraviolet radiation of wavelengths between about 290 nm and 320 nm (UV-B region) has been known to rapidly produce damaging effects on the skin including reddening or ervthema, edema, blistering or other skin eruptions in more severe cases. Prolonged or chronic exposure to radiation in this wavelength range has been associated with serious skin conditions such as actinic keratoses and carcinomas. In recent years concern has also been expressed regarding ultraviolet radiation of wavelengths above 320 nm (UV-A region) and the adverse effects of such radiation on human skin.
In view of the above, protection from the erythemal effects of sunlight produced by ultraviolet radiation within the UV-B region has been the traditional objective of sunscreen agents and compositions and as a result most compounds utilized as sunscreen agents have had light absorbance maxima within this UV-B region. Recently, as a result of growing concern for damage to the skin in the UV-A region, compounds capable of absorbing ultraviolet radiation in this region of the spectrum are becoming increasingly desirable but are generally unavailable.
Currently, the most widely utilized commercial sunscreen agents include para-amino benzoic acid derivatives, oxybenzones, methoxycinnamates and salicylates.
A desirable sunscreen agent should have absorbance maxima in the range of between 290 nm and 350 nm; have a molar absorptivity of greater than 10,000; be non-toxic, colorless and odorless; be heat and light stable; be water-insoluble and be easily and relatively inexpensively produced. While the readily available commercial sunscreen agents have enjoyed a measure of success, they all lack one or more of the above desirable properties.